linux-kernel - Re: [PATCH]: ufs: ufs_get_locked

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Message-Id: <20060801003958.c628455f.akpm@osdl.org>
Date:	Tue, 1 Aug 2006 00:39:58 -0700
From:	Andrew Morton <akpm@...l.org>
To:	Evgeniy Dushistov <dushistov@...l.ru>
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH]: ufs: ufs_get_locked_patch race fix

On Tue, 1 Aug 2006 11:30:43 +0400
Evgeniy Dushistov <dushistov@...l.ru> wrote:

> On Mon, Jul 31, 2006 at 11:02:51PM -0700, Andrew Morton wrote:
> > On Mon, 31 Jul 2006 16:57:02 +0400
> > Evgeniy Dushistov <dushistov@...l.ru> wrote:
> > 
> > Looks good to me.
> > 
> > Is there any need to be checking ->index?  Normally we simply use the
> > sequence:
> > 
> > 	lock_page(page);
> > 	if (page->mapping == NULL)
> > 		/* truncate got there first */
> > 
> > to handle this case.
> 
> Yes, I made it in analogy with `find_lock_page' and missed fact
> that if we increment usage counter of page, we have no need to check
> page->index.

OK.  find_lock_page() has the splice stuff in it.

> Need another patch?

Is OK, I updated it.

I'm not sure that the `goto repeat' is needed if truncate got there first,
really - if truncate took the page down then it's now outside i_size and
shouldn't be coming back.

If the page _can_ come back then this code is all rather problematic. 
Because this means that the page can come back (via an extending write())
one nanosecond after ufs_get_locked_page() returns NULL.  Won't the callers
of ufs_get_locked_page() get confused by that?

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